What is a Trunnion Mounted Ball Valve?

A Trunnion Mounted Ball Valve is a quarter-turn valve with a spherical closure unit (the ball) supported by trunnion bearings at the top and bottom. Unlike Floating ball valves, the ball in a trunnion valve is fixed and does not move axially but rotates only. Sealing is achieved by seat rings which are spring or pressure loaded against the ball. This robust design is ideal for high-pressure and large-bore line services, reducing the operating torque and lowering the risk of valve failure under extreme conditions.

• Ball: The central closure element, usually precision machined, supported on two trunnions.
• Trunnion Support: Bearings or shafts supporting the top and bottom of the ball, minimizing side loads and operational torque.
• Seats: Spring or pressure loaded against the stationary ball for reliable sealing.
• Body: The outer valve enclosure, typically metallic, built per relevant industry standards such as API 6D or ASME B16.34.
• Stem: Responsible for rotating the ball via actuator or lever to open/close the valve.

Trunnion mounted ball valves excel in pipelines transporting oil, natural gas, petrochemicals, and other high-pressure/hazardous flows.

Operating Principle of Trunnion Ball Valves

The trunnion mounted ball valve operates on a simple yet robust mechanical principle:

1. In the open position, the ball’s bore aligns with the pipeline, allowing fluid to pass through freely.
2. The top and bottom trunnions constrain the ball, preventing axial movement under high pressures.
3. To shut off, the valve handle (or actuator) turns the stem, which rotates the ball 90°. The flow path becomes perpendicular to the bore, fully blocking the passage.
4. Sealing force is provided by springs or the pipeline pressure pushing the seat rings onto the ball for bubble-tight shutoff.
5. Low operational torque is maintained even at higher pressures compared to floating ball valve designs.

Trunnion Mounted Ball Valve Design Standards Overview

Internationally recognized trunnion mounted ball valve design standards ensure valves deliver uniform performance, safety, interoperability, and quality. These standards are established by authoritative bodies such as API (American Petroleum Institute), ASME (American Society of Mechanical Engineers), ISO (International Organization for Standardization), and others. Adoption of these standards is often mandated by regulatory authorities and industry best practices.

Key Concepts in Ball Valve Standards

• Pressure Ratings: Maximum allowable pressure at specified temperature conditions (often by class: e.g., ANSI 150, 300, 600, etc.)
• End Connections: Flanged, butt-weld, socket weld, threaded, or special connections per ASME/ISO standards.
• Face-to-Face Dimensions: Standardized dimensions allow interchangeability and compatibility across installations.
• Material Compatibility: Defines required properties and selection criteria for body, trim, seats, and seals.
• Testing Requirements: Mandates pressure, leakage, and functional testing procedures under specified conditions (hydrostatic, pneumatic, etc.).
• Design Calculations: Includes wall thickness, seat sealing force, and safety factors.

Below is a summary table of the main design standards applied to trunnion mounted ball valves:

List of Major International Ball Valve Standards

For trunnion mounted ball valves, the following standards are among the most widely specified in global projects. Referencing these standards ensures optimal safety and compliance:

Material Requirements and Specifications

Proper material selection is fundamental for the design and performance of a trunnion mounted ball valve. Below are typical material specifications as required or referenced by industry standards:

Valves designed per API, ASME, or ISO standards require full documentation and traceability of materials, often with supporting Mill Test Certificates (MTC) and NACE MR0175/ISO 15156 compliance for sour service applications.

Trunnion Ball Valve Design Considerations

Adherence to trunnion mounted ball valve design standards entails several important engineering considerations:

1. Pressure Containment & Wall Thickness

• Wall thickness must be calculated according to ASME B16.34 or API 6D charts, including allowances for corrosion and manufacturing tolerances.
• Body and bonnet dimensions and pressure class to correspond with system MAWP (maximum allowable working pressure).

2. Seat and Seal Design

• Soft-seated (PTFE, RPTFE, Devlon) vs. metal-seated (Stellite, Inconel) are selected based on media, temperature, and shutoff requirements.
• All seats and seals must be fire-safe coded if installed on hydrocarbon services (API 607 or ISO 10497 compliance).
• O-rings and gaskets must resist process chemicals and temperature extremes.

3. Trunnion Support and Bearings

• Trunnion shafts must provide low-friction, reliable support even under rapid cycling.
• Bearings/flange geometry to minimize stem or trunnion wear, reduce operation torque, and prevent galling.

4. Antistatic and Blowout-Proof Features

• Standards require electrical continuity (antistatic device) between ball, stem, and body to prevent sparking.
• Blowout-proof stem design ensures the stem cannot be ejected from the valve under full internal pressure.

5. Drain and Vent Capabilities

• Large trunnion valves often feature body drain and vent ports (in compliance with API 6D or ISO 14313), vital for testing, maintenance, and safety.

6. End Connections & Face-to-Face

• Conformance with ASME B16.5 (flanged), B16.11 (socket/threaded), B16.25 (buttwelds), and B16.10 (face-to-face) is standard.

7. Fire Safety

• Fire-tested valves per API 607 / ISO 10497 are a must, especially in oil and gas service to ensure shut-off capability after fire exposure.

8. Fugitive Emissions

• Meeting ISO 15848 or API 622 for low leakage ensures environmental compliance and process safety.

Key Advantages of Trunnion Mounted Ball Valves

Adoption of trunnion mounted ball valve design standards unlocks several operational and safety benefits:

• Low Operating Torque: Trunnion mount and seat design dramatically lower torque requirements, ensuring ease of actuation, even at large diameters and high pressures.
• Reliable Sealing: Spring or pressure loaded seats deliver bubble-tight shutoff (per API 6D) even with pressure fluctuation or thermal cycling.
• Long Lifecycle: Minimization of ball/seat wear due to trunnion support, resulting in higher durability and fewer maintenance intervals.
• High Pressure Performance: Suitable for API 150

  up to 2500

  and higher (as per ASME B16.34/ISO 17292), performing reliably in severe service/critical isolation.

• Large Size Range: Preferred for NPS 2” (DN 50) and above up to NPS 60” (DN 1500) due to efficient force distribution and limited risk of ball displacement.
• Compliance and Interchangeability: Standardization ensures valves fit global project specifications, promoting cross-brand compatibility and easier logistics/sourcing.
• Fire-safe and Emissions Standards: Certified valves maintain sealing even after fire or in service with hazardous media as required by leading regulatory standards.
• Bi-directional Shutoff: Most trunnion ball valves offer tight shutoff in both flow directions per API 6D/ISO 14313.

Common Applications and Use Cases

Trunnion mounted ball valves, compliant with international design standards, are vital in sectors requiring critical isolation, tight shutoff, and resilience under severe service. Representative applications include:

• Oil & Gas Transmission Pipelines: Mainline isolation, block valves, pig launcher/receiver shutoffs; high-pressure, large-diameter lines (API 6D/ISO 14313 critical).
• Refineries and Petrochemical Plants: Product isolation, emergency shut-off (ESD), process unit block valves, underground storage.
• Marine and Offshore Installations: FPSO, subsea manifolds, topside production; must comply with fire & API 6D/ISO 17292 standards.
• Power Generation: Combined cycle gas turbine and thermal plants; fuel/water/feedwater line isolation.
• Gas Distribution & LNG Terminals: High cycle, large bore isolation in LNG, CNG regasification, or distribution manifolds.
• Chemical and Fertilizer Plants: Handling corrosive, dangerous, or abrasive media; often with metal-seated designs.
• Mining & Slurry Transport: Abrasive and high-solid pipelines; tough seats, durable trim necessary.
• Fire Protection Systems: Main control and isolation points in hydrocarbon terminal firefighting headers.

Pressure/Temperature Ratings & Technical Tables

The pressure-temperature rating of a trunnion mounted ball valve is determined per the design standard, usually following ASME B16.34 or API 6D rating tables. Below is a representative table (for Carbon Steel ASME 150

-2500

valves):

Note: Always confirm the exact pressure-temperature chart for the selected valve material as required by project or regulatory specifications.

Typical Trunnion Ball Valve Specification Table

A general specification outline for a trunnion mounted ball valve as per principal design standards might be as follows:

Maintenance, Inspection, and Safety Standards

Proper maintenance and safety protocols for trunnion mounted ball valves, especially in critical service, are specified in international and regional codes. These often include:

• API 6D/ISO 14313: Mandates periodic function testing and on-site inspection protocols for pipeline valves.
• API 598: Valve inspection and testing procedures, supplementing or paralleling main manufacturing standards.
• MSS SP-61: Standardizes hydrostatic and air test methods for steel valves.
• Fugitive Emissions Monitoring (ISO 15848): Routine emission measurement requirements for valves in environmentally sensitive/regulated installations.
• Replacement & Upgrade: Any modifications or repairs must use components traceable to certified standards.
• Lock-out/Tag-out (LOTO): Essential for safety during maintenance as per OSHA or local regulatory codes.

Compliance & Certification Requirements

Trunnion mounted ball valves must be provided with full compliance certifications, clearly referencing:

• Design Certificate: Stating all applied standards (API 6D, ASME B16.34, ISO 14313, etc.).
• Mill Test Certificate (MTC): For every pressure part in accordance with EN 10204 (usually 3.1 or 3.2).
• Test Reports: Including results of hydrostatic, seat, air, fire-safe, emission, and antistatic tests.
• Marking Requirements: Per API/ASME codes, specifying pressure rating, material, serial number, standard reference, etc.
• Environmental & Safety Certifications: For hazardous or environmentally sensitive service – ISO 15848, PED (Pressure Equipment Directive), ATEX (where required).
• NACE Compliance: MR0175/ISO 15156 for sour oil and gas fields (H2S resistance).
• Traceability: Full records of part origin, heat numbers, and test documents must be maintained for the lifecycle of the valve as per operating company protocols.

Frequently Asked Questions: Trunnion Mounted Ball Valve Standards

Q1: What is the difference between API 6D and ISO 14313?

API 6D and ISO 14313 are essentially harmonized standards. API 6D is predominant in North America, while ISO 14313 is used internationally and in global projects. Both address the design, manufacturing, testing, and documentation of trunnion mounted ball valves for pipelines.

Q2: Are trunnion ball valves always fire-safe?

No, fire-safety is mandatory only when valves are used for flammable or hazardous service. The valve must pass certification per API 607 or ISO 10497 to be officially declared “fire safe”. For non-hydrocarbon or water service, this may not be a requirement.

Q3: How are trunnion ball valves sized?

Valve size (NPS/DN) is determined by pipeline bore and flow capacity needs. For pipeline service, sizing follows project P&ID, maximum flow rates, and applicable codes (ASME B16.10 for face-to-face, API 6D for end connections, etc).

Q4: What’s the main sealing difference between floating and trunnion ball valves?

Floating ball valves rely on upstream pressure to push the ball against the downstream seat for sealing (best for smaller sizes/pressures). Trunnion ball valves use trunnion supports and seats loaded by springs or pressure, providing reliable, low-torque operation at large diameters and elevated pressures.

Q5: Do all trunnion ball valves have double block and bleed capability?

Not all, but many API 6D/ISO 14313 designs specify double block and bleed (DBB) as standard, meaning both upstream and downstream seats can seal independently, with a provision to bleed the cavity between for verification/testing.

Q6: What is NACE MR0175/ISO 15156, and when is it relevant?

NACE MR0175/ISO 15156 governs material selection for resistance to hydrogen sulfide (H2S) cracking (“sour service”). Trunnion valves used on sour oil & gas streams must comply, both for base materials and weld overlays.

Q7: Which tests are mandatory before installing a trunnion ball valve?

Mandatory factory tests include: hydrostatic shell and seat test, low-pressure air seat test, functional operation test. For hazardous or critical services, fire-safe and fugitive emissions testing per project directives may be required.

Q8: Can trunnion mounted ball valves be automated?

Yes, most are designed with mounting flanges per ISO 5211 or equivalent, enabling direct attachment of pneumatic, electric, or hydraulic actuators as specified by operational requirements.